Windows 10 will have grabbed between 19% and 21% of the personal computer operating system market by its one-year anniversary, putting Microsoft a third of the way toward its goal of 1 billion devices, according to an analysis of the upgrade's uptake rate so far.

Data published last week by analytics vendor Net Applications pegged Windows 10's user share -- an estimate of the percentage of the world's computers that run individual operating systems -- at 14.2% for March, an increase of 1.3 percentage points over the month prior.

Eight months after its launch, Windows 10 powered about 15.6% of just those PCs running Windows; the percentage among Windows systems was higher than for all machines because Windows ran on 90.5% of the world's PCs, not 100%.

The average Windows 10's growth over the last three months was 1.4 percentage points per month, while the average over the last six months was 1.3 points. With those trends in place, a forecast for 10's user share come the end of July -- when the OS reaches its first anniversary -- can be calculated.

Using the six-month average, Windows 10 will end July at 19.2%, while plugging in the three-month average results in 20.6%.

Both numbers would be slightly ahead of Windows 7's one-year mark of 18.9%, again illustrating that while Windows 10 -- as Microsoft has repeatedly claimed -- may be the fastest-growing version of Windows ever, it has not overturned historical adoption trends. That's true even with the company's notable free upgrade offer to millions of customers.

When only Windows systems are considered, 10 would account for approximately 21.3% of all Windows-powered PCs by the end of July under the more conservative six-month growth rate. Using the larger average gains over the last three months, Windows 10 would be on a 22.8% share of all Windows machines.

Those figures, in turn, translate into between 308 million and 342 million personal computers running Windows 10, assuming that Microsoft's often-cited 1.5 billion Windows PCs is accurate. That means Microsoft will be a third of the way toward meeting its self-imposed goal of 1 billion Windows 10 devices by mid-2018.

Surprisingly, the upper end of the 308-342 million range is close to what Computerworld forecast in February 2015, when it pegged approximately 358 million Windows 10 PCs at the one-year anniversary. At that time, Computerworld based its projection on the performance of Windows 8.1, the free upgrade Microsoft shipped in October 2013 as the follow-up to the original Windows 8 of 2012.

That Computerworld's prognosis was even close to the mark said less about divination skills and more about dumb luck: The crude estimate relied on several dartboard premises, including that Windows 7 users would rally to the free upgrade at a rate of about half that of Windows 8.1's uptake.

In fact, Windows 7 users have upgraded -- and if past trends continue, will keep upgrading -- at a rate very near Computerworld's assumption, but Windows 8 and 8.1 users have lagged behind their upgrade-to-10 expectations. (The failure of Computerworld's model on 8/8.1 -- which concluded that two-thirds of all Windows 8 and 8.1 users would upgrade within a year's time to Windows 10 -- accounts for the gap between the low-end forecast of 308 million PCs running Windows 10 by July 31 and the 358 million predicted in 2015.)

Forecasting even further out with Net Applications' data, which by nature is imprecise and subject to the vagaries of the firm's methodology, has been iffy at best. But its crystal ball hints that Windows 10 will account for about one-fourth of all personal computer operating systems by the end of 2016, or at the 18-month mark. Previously, Computerworld bet that Windows 10 would reach the one-quarter yardstick within 13 months.

The data points to more than just prognostication abilities, but also -- assuming Microsoft's internal forecasting is similar -- why the company has turned up the upgrade heat on consumers and small businesses. Without the aggressive push, which was still a secret in early 2015, it's almost certain that Windows 10 would not be where it is today.

It's unknown whether Microsoft will extend the free upgrade offer, a tactic it could deploy to continue pressing adoption of the new OS. What has become clear is that the free upgrade has not dramatically changed the growth rate of Windows 10 from that of Windows 7, the most logical comparison. If Microsoft expected the offer to result in a substantial lead over Windows 7's trajectory, it's been disappointed.

The ball, of course, is in Redmond's court.

Data: Net Applications

Computerworld's forecast puts Windows 10 on about 21% of all Windows PCs by the end of July, the operating system's one-year anniversary.

This story, "Windows 10 forecast: On as many as 342M PCs at one-year mark" was originally published by
Computerworld.